Corrugated paperboard is typically used in many different applications, for example, to form containers, boxes, cartons, or dividers for holding, storing, stacking or shipping various items such as agricultural produce.
Typically, such containers have a bottom panel and four side walls, and are formed from a blank scored with score lines or cut lines. The containers are frequently open-topped containers, with male member stacking tabs extending upward from the top edges of the side walls and complimentary female member cut-out slots in the bottom panel or side wall of the container. During use, the stacking tabs of an open-topped container may be inserted into the slots cut out of an adjacent container, thereby enabling stacking of the containers on top of one another.
Such stacking of adjacent containers is only possible if the pattern of the cut-out slots are configured in the same pattern as the stacking tabs. This is made easier by the fact that such tabs and cut-out slots are, with increasing frequency, configured in a common footprint, such that the pattern and placement of the tabs and slots follow an industry standard.
When shipping or stacking open-topped containers, the top container in stack, or an individual container not in a stack, is left uncovered. In these circumstance, a dust cover, which is a flat piece of flexible material that is flexible enough to bend but firm enough to create firm frictional connections, such as paperboard, is often placed on top of the open container. The dust cover mimics the bottom panel of an adjacent container, as if it were separated from the container's side walls. It is usually a substantially rectangular corrugated paperboard with several cut out slots configured in a common footprint to accept the stacking tabs of an open-topped container.
Problems arise when the cut out slots do not accept the tabs in a firm and secure manner. This creates loose fitting stacks that are prone to toppling, or loose fitting dust covers that are prone to easy and premature removal. As a result, some slots are coupled with friction locks, wherein an extension of the bottom panel or dust cover presses against the tab as it extends through the cut out slot, creating a positive frictional force between the lock and the tab.
However, these friction locks have a short life span. Frequent use and re-use of the locks lowers the ability of the locks to maintain strong frictional contact with the stacking tabs. This diminished capacity often comes in the form of fraying or disfigurement of the lock, which prevents the lock form being able to adequately press against the tab. Further, tab locking mechanisms are inwardly spaced a small margin from the edge of the bottom panel or dust cover, leaving a small strip of paperboard between the edge and the lock. Much like the locks themselves, the narrow strip of flexible material that lies between the lock and the edge of the bottom panel or dust cover often frays and wears out, further loosening the connection.
Further, prior art friction locks can only contact the tabs if the tabs are of sufficient thickness such that they rub against the lock. This creates a problem when the tabs are thin enough so that they extend through the cut out slot without significantly touching the friction lock. In these circumstances the lock's functional capacity is impaired, as there is insufficient friction to hold the tab in place securely. Along similar reasoning, variations in the size of the open-topped container are problematic, as the locks can only accept tabs of an exact formation. Thus, a container that is slightly thinner, for example, by ⅛ of an inch, requires an entirely different dust cover with locks inwardly spaced an additional ⅛ of an inch to achieve proper friction locking.
Therefore, it is an object of this invention to provide a friction lock that has sufficient durability to sustain frequent use and can securely hold stacking tabs of various thicknesses and from containers of various widths.